1. Field of the Invention
The present invention relates to a transport system and a transport method.
2. Description of the Related Art
As a transport system to be applied to, for example, a semiconductor manufacturing plant, a known transport system includes a track, a plurality of transport vehicles that travel along the track and convey a transported object to at least a station, and a controller that performs communication with the respective transport vehicles and controls the behavior of the respective transport vehicles (for example, see Japanese Patent No. 5309814).
In the above-described transport system, when a grip-load request to acquire the transported object from the station is present, the controller provides a transport command corresponding to the grip-load request to the transport vehicle. In terms of improving the conveying efficiency of transported objects to the station, when another transport vehicle that is able to receive the transport command and that arrives at the station earlier than the transport vehicle to which the transport command has been provided is newly detected, the controller may perform command swap processing in which the transport command is newly provided to the newly detected transport vehicle after transmitting a delete command to delete the transport command to the transport vehicle to which the transport command has been provided earlier.
In the command swap processing, however, the transport vehicle to which the transport command has been provided earlier may be unable to receive the delete command. Also, even when the transport vehicle transmitted to the controller a response that the delete command has been received, the controller may be unable to receive the response. In such a case, the controller is unable to determine whether the transport command is in a state of being provided to the transport vehicle to which the transport command has been provided earlier, and unable to provide the transport command to the transport vehicle that arrives first at the station.